To register for a Zotero account, go to Zotero.org and click on 'Register' at the top right of the screen.
Create a username and password. Zotero will send you an email to confirm your account.
This will help you sync your content and settings across all devices through which you access Zotero (whether browser-based or standalone) as well as enable you to access your content through the Zotero website when on a device that does not or cannot have Zotero installed.
You can use Zotero with Firefox, Chrome, or Safari. There is no version compatible with Internet Explorer.
If you are predominantly a Firefox user, download Zotero for Firefox. If you prefer to use Chrome or Safari, download the Zotero Standalone and the appropriate connector for your browser. The standalone version works the same way as the Firefox version, but it operates in its own window instead of within the browser.